set

, unset

, setenv

, unsetenv

, export

- shell built-in functions to determine the characteristics for environmental variables of the current shell and its descendents

Synopsis

sh

set [--aefhkntuvx [argument]]...

unset [name]...

export [name]...

csh

set [var [= value]]

setvar [n] = word

unsetpattern

setenv [VAR [word]]

unsetenvvariable

ksh

set [±abCefhkmnopstuvx] [±o option]... [±A name]
[arg]...

unset [-f] name...

**export [name [=value]]...

**export [-p]

Description

sh

The set built-in command has the following options:

--

Does not change any of the flags. This option is useful in setting $1 to -.

-a

Marks variables which are modified or created for export.

-e

Exits immediately if a command exits with a non-zero exit status.

-f

Disables file name generation.

-h

Locates and remembers function commands as functions are defined. Function commands are normally located when the function is executed.

-k

All keyword arguments are placed in the environment for a command, not just those that precede the command name.

-n

Reads commands but does not execute them.

-t

Exits after reading and executing one command.

-u

Treats unset variables as an error when substituting.

-v

Prints shell input lines as they are read.

-x

Prints commands and their arguments as they are executed.

Using + rather than - causes these flags to be turned off.
These flags can also be used upon invocation of the shell. The
current set of flags can be found in $-. The remaining arguments are
positional parameters and are assigned, in order, to $1, $2, . . . . If
no arguments are given the values of all names are printed.

For each name, unset removes the corresponding variable or function value. The
variables PATH, PS1, PS2, MAILCHECK, and IF cannot be unset.

With the export built-in, the given names are marked for automatic export
to the environment of subsequently executed commands. If no arguments are given,
variable names that have been marked for export during the current shell's execution
are listed. Function names are not exported.

csh

With no arguments, set displays the values of all shell variables. Multiword
values are displayed as a parenthesized list. With the var argument alone,
set assigns an empty (null) value to the variable var. With arguments of
the form var = valueset assigns value to var, where value is one
of:

word

A single word (or quoted string).

(wordlist)

A space-separated list of words enclosed in parentheses.

Values are command and filename expanded before being assigned. The form set var[n]=word
replaces the n'th word in a multiword value with word.

With no arguments, setenv displays all environment variables. With the VAR argument,
setenv sets the environment variable VAR to an empty (null) value. (By convention,
environment variables are normally given upper-case names.) With both VAR and word
arguments specified, setenv sets VAR to word, which must be either a
single word or a quoted string. The PATH variable can take multiple word
arguments, separated by colons (see EXAMPLES). The most commonly used environment variables,
USER, TERM, and PATH, are automatically imported to and exported from the csh
variables user, term, and path. Use setenv if you need to change
these variables. In addition, the shell sets the PWD environment variable from
the csh variable cwd whenever the latter changes.

The environment variables LC_CTYPE, LC_MESSAGES, LC_TIME, LC_COLLATE, LC_NUMERIC, and LC_MONETARY take immediate
effect when changed within the C shell. See environ(5) for descriptions of
these environment variables.

unsetenv removes variable from the environment. As with unset, pattern matching is
not performed.

ksh

The flags for the set built-in have meaning as follows:

-A

Array assignment. Unsets the variable name and assigns values sequentially from the list arg. If +A is used, the variable name is not unset first.

-a

All subsequent variables that are defined are automatically exported.

-b

Causes the shell to notify the user asynchronously of background job completions.

-C

Prevents existing files from being overwritten by the shell's > redirection operator. The >| redirection operator overrides this noclobber option for an individual file.

-e

If a command has a non-zero exit status, executes the ERR trap, if set, and exits. This mode is disabled while reading profiles.

-f

Disables file name generation.

-h

Each command becomes a tracked alias when first encountered.

-k

All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.

-m

Background jobs run in a separate process group and a line prints upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.

-n

Reads commands and checks them for syntax errors, but does not execute them. Ignored for interactive shells.

+o

Writes the current option stettings to standard output in a format that is suitable for reinput to the shell as commands that achieve the same option settings.

-ooption

The option argument can be one of the following option names:

allexport

Same as -a.

errexit

Same as -e.

bgnice

All background jobs are run at a lower priority. This is the default mode. emacs Puts you in an emacs style in-line editor for command entry.

gmacs

Puts you in a gmacs style in-line editor for command entry.

ignoreeof

The shell does not exit on end-of-file. The command exit must be used.

keyword

Same as -k.

markdirs

All directory names resulting from file name generation have a trailing / appended.

monitor

Same as -m.

noclobber

Prevents redirection operator > from truncating existing files. Requires the >| operator to truncate a file when turned on. Same as -C.

noexec

Same as -n.

noglob

Same as -f.

nolog

Does not save function definitions in history file.

notify

Same as -b.

nounset

Same as -u.

privileged

Same as -p.

verbose

Same as -v.

trackall

Same as -h.

vi

Puts you in insert mode of a vi style in-line editor until you hit escape character 033. This puts you in control mode. A return sends the line.

viraw

Each character is processed as it is typed in vi mode.

xtrace

Same as -x.

If no option name is supplied then the current option settings are
printed.

-p

Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid is not equal to the real uid, or when the effective gid is not equal to the real gid. Turning this off causes the effective uid and gid to be set to the real uid and gid.

-s

Sorts the positional parameters lexicographically.

-t

Exits after reading and executing one command.

-u

Treats unset parameters as an error when substituting.

-v

Prints shell input lines as they are read.

-x

Prints commands and their arguments as they are executed.

-

Turns off -x and -v flags and stops examining arguments for flags.

–

Does not change any of the flags. This option is useful in setting $1 to a value beginning with -. If no arguments follow this flag then the positional parameters are unset.

Using + rather than - causes these flags to be turned off.
These flags can also be used upon invocation of the shell. The
current set of flags can be found in $-. Unless -A is
specified, the remaining arguments are positional parameters and are assigned, in order, to
$1$2 . . .. If no arguments are given then the names and
values of all variables are printed on the standard output.

The variables given by the list of names are unassigned, that is,
their values and attributes are erased. readonly variables cannot be unset. If
the -f flag is set, then the names refer to function names.
Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes
their special meaning even if they are subsequently assigned.

When using unset, the variables given by the list of names are
unassigned, i.e., their values and attributes are erased. readonly variables cannot be
unset. If the -f, flag is set, then the names refer to
function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and
_ removes their special meaning even if they are subsequently assigned.

With the export built-in, the given names are marked for automatic export
to the environment of subsequently-executed commands.

When -p is specified, export writes to the standard output the names
and values of all exported variables in the following format:

"export %s=%s\n", name, value

if name is set, and:

"export %s\n", name

if name is unset.

The shell formats the output, including the proper use of quoting, so
that it is suitable for reinput to the shell as commands that
achieve the same exporting results, except for the following:

Read-only variables with values cannot be reset.

Variables that were unset at the time they were output are not reset to the unset state if a value is assigned to the variable between the time the state was saved and the time at which the saved output is reinput to the shell.

On this man page, ksh(1) commands that are preceded by one or
two * (asterisks) are treated specially in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.

I/O redirections are processed after variable assignments.

Errors cause a script that contains them to abort.

Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

Examples

csh

The following example sets the PATH variable to search for files in
the /bin, /usr/bin, /usr/sbin, and /usr/ucb/bin directories, in that order: